Evolutionary trends in the epithecate scleractinian corals
EWA RONIEWICZ and JAROSLAW STOLARSKI
Roniewicl, E. & Stolarski, J. 1999. Evolutionary trends in the epithecatc scleractinia" corals. -Acta Palaeomologica Po{onica 44, 2,131-166.
Adult stages of wall ontogeny of fossil and Recent scleractinians show that epilheca was the prevailing type ofwall in Triassic and Jurassic corals. Since the Late Cretaceous the fre- quency of epithecal walls during adult stages has decreased. In the ontogeny of Recent epithecalc corals, epitheca either persists from the protocorallite to the adult stage, or is re placed in post-initial stages by trabecular walls that are often accompanied by extra -calicular skeletal clements. The former condition means that the polyp initially lacks the edge zone, the latter condition means that the edge zone develops later in coral ontogeny. Five principal patterns in wall ontogeny offossil and Recent Scleractinia are distinguished and provide the framework for discrimination of the four main stages (grades) of evolu tionary development oftheedge-zone. The trend ofincreasing theedge-zone and reduction of the epitheca is particularly well represented in the history of caryophylliine corals. We suggest that development of the edge-zone is an evolutionary response to changing envi rolmlent, mainly to increasing bioerosion in the Mesozoic shallow-water environments. A glossary is given of microstructural and skeletal tenns used in this paper.
Key words: Scleractinia, microstructure, thecal structures. cpitheca, phylogeny.
twa ROl1iewicz {erof/@Marda.pan.plj alUl jaros{aw Stolarski {swlacy@two,-da.pan.plj, lllstytl/t Pa/eobi%gii PAN, 11/. Twarda 51/55, PL-OO·818 WarsZGwa, Polalld.
In Memory ofGabriel A. Gill, an Eminent Student ofCoral Structllres, our Colleague alld Friend Introduction
Recent study of macroevolutionary trends in Scleractinia has focused on the develop ment of coloniality (Coates & Oliver 1974; Coates & Jackson 1985; Rosen 1986), microstructural changes of skeleton in their history (Roniewicz & Morycowa 1993), and phylogenetic differentiation based on molecular data (Romano & Palumbi 1996; Veron et al. 1996). In this paper we focus on some evolutionary aspects of the development of the edge-zone, a feature regarded by Vaughan & Wells (1943) and Wells (1956) as one of 132 Epi/hecute ScleraCIIIIIOm: RONJEWICZ & STOLARSKI the most important in the evolution of the Scleractinia. These aulhors remarked lhat development ofthe edge-zone led to a reduction ofthe epilheca and its replacement by other types ofouter wall. We auempllo trace this process using changes in wall suuc tures observed in the stratigraphic column and in the ontogeny ofsome Recent corals. Analysis of paleootological data has also led to the verification ofearlier views on the stratigraphic distribution ofepitheca. The majority of pre-Cenomanian genera have epithecalhololheca developed as a complete wall or at least as epilhccal rings (compare Koby 1881-1889. 1905: Frech 1890: Volz 1896: Vaughan & Wells 1943). The Late Triassic - Late Jurassic coral fau nas show a great taxonomic diversity of corals with solitary and phaceloid growth forms (compare Vaughan & Wells 1943), nearly all ofthem being epithecate forms. In the Late Triassic and Late Jurassic. when fine·grained shallow water calcareous sedi mentation de\'eloped, the phaceloid epithecate corals frequently predominated (Ro niewicz & Rooiewicz 1971: Stanton & Fltigel 1987, 1989: Geister & Lathuilihe 1991: Insalaco el 01. 1997). Questions arise: Whether the success ofthese corals lacking the edge-zone resulted from their special adaptations to the specific environment of the calcareous scdimentation? Which ofthe factors: physical, chemical or biological con trolled their development? What caused their reduction in the Late Cretaceous and continuation of this trend in the Cenozoic, resulting in their recent Iimitalion to relict cryptic or deep-water solhary forms? Though no defitite answers erist, we hope that our speculations will stimulate discussion. Institutional abbre\'ialiorui: GSA. Geologiscbe Bundesanstalt. Wien: ZPAL. Insti tute ofPaleobiology, Warsaw: UJ. Jagiellonian University, Cracow; MNHN, Museum National d'Histoire Naturellc, Paris: MS, Naturhistorischcs Museum. Humboldt Uni versitat. Berlin: NHM. Natural History Museum. London: USNM, National Museum of Natural History, Smithsonian Institution, Washington, D.C.: MGUWr, Geological Museum, Wrodaw University, Wroclaw.
Epithecal walls: structure and terminology
The term epitIJeco was used by Milne Edwards & Haime (I &48) for a 'skeletal sheath adhering to the external board of costae'. As examples of epitheca-bearing scler actinians they gave: Momlil'aJtia Lamouroux. 1821. BaJallophyllio Wood. 1844. and Flabellum Lesson. 1831 (in the lattcr case they noticed. however, the 'porcelain' ap pearance of thaI wall). In subsequent years, the term epilheca was used for alllrans versely folded walls ofsolitary and phaceloid corals. and a wall covering the lowercol any surface; for the epitheca of scleractinian colonies. a separate term holotheclI was later adopted (Alloiteau 1957), a term previously utilized in Rugosa and Tabulata (e.g.• Hudson 1929: Hill 1935). Alloiteau (1952) introduced a new term archaeotheca to de scribe the transversely folded 'septo-dissepimental' wall of the stylophyllids, pro cyclolitids. amphiastreids. and thecocyathids. Archaeotheca was. however. impre cisely defined (in fact. none ofthe above mentioned coral groups have a 'septo-disse pimental' wall) and structurally different walls were later described using this term (sec Stolarski 1995). Distinction between epithecal and archaeothccal walls was sup- ACfA PALAEONlULOOICA POLONICA (44) (2) 133 ported by Weyer (1975). He considered the walls developed subsequent to the septa to be epilhecal, e.g.• in scleractinian Monl/i\'a/lia caryophyl/ata Lamouroux. 1821. or in rugosan Ca/oslylis cribraria LindslrOm, 1868, while the walls developed prior to the septa to be archaoothecal, e.g.• Axosmilia or TheccH,:yalhlls maC/ms (Goldfuss. 1826) among Scleractinia. and Cyalhaxonia conlll Michelin, 1847 among Rugosa. As we show in this paper, the position of the cpithcca may vary in the ontogeny of particular species (it may be formed after or before the septa). Thus, we consider the above -presented distinction between epitheca and arch:leotheca unnecessary, and we sup port the earlier statement that the term arehaootheca should be rejected as imprecisely established and confusing (Stolarski 1995). Essential for understanding epitheca formation was a paper by Barnes (1972). He studied the epithecal wall in a range of Recent shallow-water zooxanthellate corals [/sophy//ia sinuosa (Ellis & Solander. 1786), Manici,la areaO/ala (Linnaeus. 1758), Montaslrea anl/u/oris (Ellis & Solander. 1786), Poriles aslreoides Lamarck.. 1816. Dip/oria slrigosa (Dana, 1846). Fa\'ia speciosa (Dana, 1846)] and showed that it is a two-fold, fibrous structure developing in the marginal zone of the polyp body. Barnes (1972) noted also a comparably structured wall in the azooxanthellate Gordineria. Re cent studies of the family Aabellidae (Caryophylliina). traditionally considered as epithecate corals. have shown that the wall of most genera is trabecular (margino thecal). and thus essentially different in structure from epitheca (Stolarski 1995). This encouraged us to outline precise criteria for the differentiation between epithecal walls and similar but non-homologous walls in fossil and Recent Scleractinia.
Place of formation Epitheca is formed in an anatomically specialized soft tissue marginal fold. the lappet cavity (Barnes 1972). The initial, outer layer (primary layer sellSIl Barnes 1972) is fonned in the apical pan of the lappet cavity. The inner layer may form initially in lhe lappet or behind it in a secreting zone of the body wall resulting in formation of. re spectively, thin (pellicular) or thick (mature) epitheca (see also Stolarski 1995: fig. I; Stolarski 1996: fig. I).
Morphology Epitheca constitutes the external and often the distalmost part of the corallum (Fig. IA). Generally. it is covered with transverse incremental Hoes and folds but sometimes also bears longitudinal striations (Fig. 2B. C. F). During ontogeny, epilheca may differ in rates ofdevelopment from other skeletal elements (Fig. 3A-D). Growth ofepitheca may exceed that of radial elements. thus re· suiting in the fonnation of a distal tube of epitheca (Fig. 38): or it may equal the growth ofradial elements (Fig. 3D); or be retarded in comparison with the latter (Figs 3C, IIC), resulting in epitheca coming in contact with septa-derived structures (e.g.. septotheca. synapticulotheca) and epicostal dissepiments. Epitheca may be developed as a continuous layer covering the whole corallum or its proximal pan (ontogeny of dendrophylliids); it may be reduced to epithecal rings (e.g., in Cretaceous Mom/i va/tia, Fig. JOB, or in Recent Trochoc}'athus rawson; Pourtales. 1874, Fig. 12E): or it may form 'holothecal rings' (e.g.• in Monicina af?olata. see Fabricius 1964). In corals with continuous epitheca, the living tissue is confined to the narrow lone at the .34 Epllh«ot~ uluaetimans: RONlEWlCZ & SlOLARSICI
A outer epithecaI layer (oon-trabecular)
Fig. I. Eplthecal YS. marginothe<:a1 wall - transverse seclWns. A. Epitheca in Gardinma with thick cpil~a1 slcrcome. B. Marginothel:a in f"/ulHlIllm With thICk inlc~ptaI stcrcornc. Modified from Stolarski (1997). calicular edge. and the rest ofthe corallurn is bare and exposed to the surroundings. In corals with epilhecal rings, the living tissue covers only lhe corallum surface above the most distal ring. Some morphological features commonly considered as typical ofthe epilhccal waH may also be observed in other walls. Frequently the contact zone between epitheca and septa is marked by a characteristic notch, but a similar notch may be developed at the cOntact with trabeculotheca or seplotheca e.g., in caryophylLiid genera Conotrochus. and 'CerOlOfrvch"s' (Fig. 4A. B). Also. the Jines marking the position ofthewithdraw ing edge-zone on the tectura surface ('Ceratolrochus' mag1UJghii. Fig. 48), or lines marking periodic incremental growth of lrabeculae on the eroded surface of the flabellid marginotheca may resemble epithecal growth lines (see Stolarski 1995: fig. 91, J). Doubts caused by a lack ofprecise morphological criteria may be eliminated by the use of microstructural criteria.
Microstructure Epitheca is built ofcalcareous fibres not organized into lrabeculae. Epitheca often ac companies other wall structures (trabcculotheca, septotheca), but may also form the only corollum wall. It consists of two pans: (I) Outer epithecallayer. In spite ofsome variation. the structure ofthis outer layer is similar in all Scleractinia (Fig. 28-0, F, G, I). It consists of a layer 1-2 IJm thick (Bames 1972) covered with growth lines. composed of distally oriented fibres (Figs 5e. 80) sometimes strongly inclined (rom the venical position. [n some corals. the fibres grow in longitudinal. parallel or subparallel lraclS. Within the lracts the fibres may form a fanwise pattern (Fig. 28).
(2) Inner epithecal layer. This layer, of variable thickness. is built of radially ar4 ranged fibres. and il grows centripetally into available intracalicular space (e.g., Figs 3E. F. 50, 68. 70, IIA).1t is an epithecal stereome, which in trabecular corals may be continuous structurally with interseptal stereome. in non-trabecular corals (Stylo phyllina). the epithecal stereome of fibro-radial structure differs microstructurally from the rest ofthe stereomal deposit that forms septa. interseptal stereome and adaxial wall stereome. and which is organized into bundles of fibres and scales and grows by ACfA PALAEONTOLOGICA POLONICA (44) (2) 13'
Fig. 2. External surface of lhe cpilheca. A. Clodophyllio m"wr Beauvais, 1967, Jurassic (Bathonian). Fairford, Glouccslcrshire, England, NHM R.%39. Sharp cpilhecaJ rims of the calices. 8. Clodophyllill cf. exctlsa (Koby, 1888), Jurassic (Kimmeridgian), CumogJowy (Pomerania. Poland), MB K..351. EpilhccaJ calieular rim with some modular SU\lCl1Jfe of lhc wall; note minulc Ioogillw:linal striatioo. C-E. 50'10 phyllopsu rugosa (Duncan. 1868). Early JurasSIC, England. C. NHM R.13332. A fagmcnl of lhc COfallue surface wIth the same suuctunl1 feawmo as abo\"C. D, E. NHM R.3194. Luera! and dislaI views of lhc conl.Ium. NOlC sharp ca1Jcu1ar nm IftSCDI In E. r. GanlWnD haI.'tlJ~fUlS Vaughan. 19«1, R~ 22"IS'ZS"N/I59"Z3'IS"W,497-541 m. hokJcype. USNM 20731. Note barnacle's bonngs Ul cpttbca. G, H. CIUtIIOIItU sp.. Creuoeous (Senoman). AuSUla, UJ 82NI. DIstal and Iowcf corallum views. Lo~'eJ surface with concentric epilhc:cal wnnkks. l J. AspuflM:1lS $p.. Crelaccous (CcnomaniaD), Egypl.1J>AL H.xVIUI. Distal (I) and lower surface of lhc colony (J), wIth Iowcf surface slightly concentrically stnIClured. 136 Epi'fu!cat~ scluoclinians: RONIEWICZ & STOLARSKI
Fig. 3. PoIyt;)'Clfhus mutl/u(l~ (Abel, 1959), Recent, M~ilIe. ~ubmarHle cave, 'Grotlc du Figuier", 12 m. A. ZPAL H.XVll/2. Early juvenile slage with cililhecal wall. Ii, ZPAL II.XVIU3. A calice with lube-like extension of me epilheca. C. ZPAL H.XVIU4, Adult septothecate condlilc with epithe<:a suppressed in its lower pan. D. ZPAL H.XVIU5. Adult. scplothecatccorallite with a thin epllheca reaching lhecalicularrim. E. F. ZPAL H.XVI1l6. Epllheca m trans\'erse KCUon, etched surface. Cenlnpelally oriented fibres W-en larged fragment of E). ACfA PALAEONTOLOOICA POLONICA (44) (2) IJ7 accretion (Roniewicz 1989a: p. 117). In thin sections of fossil material, only the inner epithecaJ layer is easily recognizable. Microstructural and morphological criteria a1Jow for the differentiation of epithecal wall from other wall structures such as tectum and marginotheca (Fig. IB). It is notewor thy that thin, pellicular epitheca in contact with epicosla1 dissepimenlS has been inter preted as a paratheca e.g., in Momli\'olr;a (Vaughan & Wells 1943: Alloiteau 1952. 1957) orin 11lecosrnilia, lkrmosmilia and Ca/omophylliopsis (Roniewicz 1966. 1976).
Types of epithf(:al walls Epitheca may form simple walls or composite waUs.
Simple walls. - In simple walls we distinguish pellicular epitheca and matllre epit1leca. These descriptive terms have been used to indicate a differences in relative thinckness of the inner epithecallayer, i.e. epithecal stereome. PelliclIlar epit1leca is the most common epithecal wall in the Scleractinia. It is a thin, transparent coating present in early onlOgenetic stages, and continues in many corals 10 be present until adult stages; its inner layer, epimecal stereome, is weakly de veloped. Pellicular epitheca may bedeveloped as an independent wall or as an element ofcomposite walls (see below). Examples include the wall in phaceloid Reriophyllia (Triassic, Fig. 6C), and pellicular holotheca in numerous colonial corals (e.g.. Man;· Clna, Recent, Fig. IIC, D). Pellicular epithecal stroctures are developed as epicostal rings in different coml groups from the Middle Jurassic onwards (see below). Matllre epit1leca has a thickened inner layer ofepithecal stereome that oflen incor porates external edges of the radial elemenlS. The following examples show the spec trum of mature epithecal struCfUres: In Volzeia subdidlOtoma (MUnster, 1839). Triassic. although the inner layer is rela tively thin, it incorporates peripheral edges ofradial elements (Fig. 6D). [n V. badiotico (Volz, 1896), Triassic, lhe radial elements are deeply embedded in thick epitheca. The internal surface ofthe epitheca is well separated from the interseptal stereome fonned by strongly elongate, centripetally growing fibres. In Protohererastraea Jeonhardi (Voll.. 1896). Triassic, the inner layer is formed from fibres generally oriented centripetally with some distal declination. At the perimeter are numerous and well defined centres of cenlripelaUy radiating fibres. In transverse sec tions ofthe wall. a complicated picture is seen. with more than ODe generation ofradiat ing fibres. Septa are deeply embedded in the wall (Fig. 7A. B). Recent Gardilleria has essentially a similar wall (Fig. 7E. F: see also Stolarski 1996: figs 4H. 1. 5A-G). In Craspedophy//ia a/pina (LorelZ, 1875). Triassic. the epithecal wall incorporating the peripheral parts of radial elements is much more folded lhan in Proto1leteraslrea (Fig. 6A, B). A similar slyle of folding has been observed in some Recent Guyniidae (Stolarski 1997) and Madracis (Fig. 5A, B). In post-Triassic corals. mafUre epithcca with embedded septa is known in C/alJo phyllia (Jurassic-Cretaceous. Morycowa & Roniewicz 1990: pI. 15; Ie, pI. 16; 1a). Genera of the C/lijia group (Triassic) represent a different structural specialiUltion from those discussed above. The epithecal wall does not incorporate septa at all. lon gitudinal structures ofequal size are fonned on the internal wall surface. They are tri- 138 £pithuDlt scltracriniulI.1: RQNlEWICZ & STOLARSKI
Fig. 4. 'OralOlllJduu' IfIQgnaglul Cc:cdwu. 1914, Recent, Marseille. submanDe cave. 13 m - species resem bling an eplthecal Gonimma but OO\'emt WIth tluck. wnnkled teenInl. A. ZPAL H. XVlV7. dislaJ VIeW. 8. MagniflCd fragment of the same spc:cmletl In lateral VIew, C. D. ZPALI1XVIIl8. etched. uansversesecuons. Explanalions: S- sep!uln IllCQrporme
Ower epl1beca1layer - dIStally oneotod fibres at the cahcular run. laleral view. Etched surface_ D. ZPAL H.XV1V11 Eplthecal Slereome - cenlripcl.a1ly onenled fi~,lranSvcDesc:ction, c1chcd surface. NOIe sep rum (5) IJw l~embeddcd In succeeding layeB ofepithecal siereomc:. E, F. HopiangltJ dllrotruGosse, 1860, Recenl. Sagra (Ponugal, Alglll'Ve). caves in the tliffsoulh of POnta da Baleeira. 1-6 m, ZPAL H.XVIUI2. E. Cabcular '·IeW of the colony, Some of the adult, Kplodlecale Cor1llla reju'·emlte (arrowed) and fonn ep;thecaI calICeS, F Centlipelally growing epilhecal diaphragm reducing calicuJar lumen ('reJuvenes cence'). 140 Epirhecmc scluac/illiuns: RONJEWICZ & STOLARSKI
Fig. 6. A. B. Matureepitheca in Cras/~dol,lIJlllU alpmo (Lorell. 1875). Camian.ltaly. GBA Voll. collcc· lion 4402. A. Lateral view orllie epilhecaJ corallilc wall. its longitudinaJ broken section showing succes sive growth wrinkles (at right). and a contact or the epitheca and septa. B. Trnnsverse broken section wilh centripetally oriented fibres of eplthcclll stereome Il Fig 7. Matlin: ep!theca III TriassIC Protolw'tnutrwa (A. 8) and Recent Gan/i_ria (C-I-l. A. Proto Iw~nu'~a lronhan/I (VoIl.. 1896). TriUSK: (LadWaD). San easslano Beds. Forcella dl Sen San. DoklmiteS. Italy. MGUWrJSc2. Trans~'erse linn 5CCtJon showing ttuck epllhc<:a1 SlC:romc whICh HlCorp<> faIU pcnpbera1 ends of radial elcmeolS. 8. LonglludlDal thin section showing e.llemal wrinkling or the .aU (al ieft) and ttI1tnpetaily onented fibres ofepuhecal stereome. C-F. Gun/llleno paradoxa (Poonales. 1 I, Reunl, SW or Jam3.lca, GOS·S9A, Stal. 112178, ITll'Nn 19'W, 700 m, ZPAL H.XVIII. C. TtlIOS~'ene tlun section showlIlg a thick eplthecal stereomc with peripheral septal ends embedded. D Tram~erse section showing centripetally orienled fibers. etched surface. E. F. Distal (E) and lalerJI (I<") Vie"" of1be conllwn. outer layer consists of very thin. distally oriented fibres (Fig, 8E), The very thick in ner layer re\-'eals a modular sUllcture (especially well seen when slightly altered diagenetically, Fig. 98, C). The modules represent equal and large bundles of fibres '42 Ep;lh~cate sc/uuclinians: RQNIEWICZ & STOLARSKJ , .,--,.... 1 -- Fig. 8. Epilhccal wall of a pachythl:caJ type: In lnrdirwpllylluln Fill 9 Epthccal wall ora pachythccal type (continued). A. Amphi(llll(lstrllt!/l mrollt!nslS (Morycowa. 1911). ~ (1...o\l.·u Aptian). Valea Izvorul Alb (Romania), JGB 120. Thick wall with thin structural modules • 6c ~. aDd nwnerous septa at righl; polished and etched surface. 8--0. Pochysolt!rlw sp., Triassic 'LeMa ~I, AUSIria. GBA 1987,{\1/14. B. C. Modular PlIdIpoimia. see Cuif 1975 and herein Fig. 98. C). Tips of bundles form granula emerging on lhe internal wall surface. which are arranged in vertical rows or di:Ipc:r'sed f.:haotically (Fig. 8A--e). Septa are in structural continuation with wall ~ of fibres. or may be separated from the wall by a sUlure (Fig. 80). 144 Epitht!cute sc/uacliniuns: RONIEWICZ & STOLARSKJ Fig. 10. A-D. Composilccpilhecal wall in MOn/liva/lia mllltifomt;sToola. 1889. Cretaceous (Ap(ian), Bul garia, ZPAL ~I.XVWI5. Disl.II.l (A) alld lateral (8) views oflhe corallum; epithecal cover inlcmlJNcd. C. D. Transverse thin section showing thin epll!leQIlying 00 the peripheral septal edges. E. MYCdophylllQ Tt!CSI WeUs. 1973. Recent. ZPAL H-XVIVI6. Growing edge of the epltheca wllh dCitally CIneOle In the Amphiastraeidae (Jurassic--crelaceous) the external and internal wall struc tures resemble tbose in some zardinophyllids (Cretaceous Amphia~'fraea reclc Am phillu!astraell rarallellsis, Morycowa 1971: pI. 26: 19, herein Fig. 9A). In comparison with the Triassic pachythecaJ wall. me amphiastraeid wall is built of well arranged ACTA PALAEONTQLOGICA POLONICA (44) (2) 145 II. A-E. Composite epilhecal wall in Municina ana/ata (Linnaeus. 1758), Re<:ent, Bahamas. A. D. ZPAL I-lXVIUI8, broken and etched longitudinal section in SEM (A -enlargement ofthe inner epithecal ,ell. explanalJoos as in E. B. C. ZPAL U. XVWI9. Colony in upper (8) and side (C) views. Epitheca ~'en prw:mllll halfof the cOl"llllum, x 1.5. E. ZPAL H,XVWI9. Transverse thin section showing a thick ...... (sp), pellicular epilheca (e), and dissepimems developed between these two walls (d). -=du.les ofthe shape ofhorizontal spines (SeptaJdorn ofOgilvie 1896) and arranged in wanc.aI rows (Mitrodelldroll, Fig. 9E; Amphiastrea, Morycowa 1964: pI. 22: lb. c; fJi8cn:a 1975: pI. I: 2, 3; Kolodziej 1995: fig. 4: A-F). The microslntcture ofall septa (...... ~ into the wall structure. If one can judge from various patterns of diage· IIdKMJ)' altered walls, the wall structure varies considerably in the Jurassic-ereta· Amphiastraeina (compare EIi~sov~ I976b). Cam 'Ie walls. - Pellicularepitheca may join structurally with various skeletal el ~ in lbe following examples: Epltbecal·stereomal wall. In stylophylline corals (Triassic-Lias), the wall is CO!!Ilp""C'd ofmicrostructurally discontinuous parts: the epithecal inner layer contacts ~ SIa"eOmedeposit built ofmultidirectionally oriented bundles and scaly fibre ag po",'" fsee Glossary: non-trabecular or fascicular corals). 146 £pithectJle sduactinians: RONIEWICZ & STOLARSKI (b) Epithecal- Eplthecal Scleractinia In stratigraphical succession Triassic The earliesl (Anisian) Scleraclinia were highly diverse, taxonomically and morpho logically. Four microstructuraVmorphological patterns ofcoral skelelon characterized four main phylogenelical stems, lhree of which are of a subordinal rank and lraceable from lhe Triassic onwards. These are: (I) the pachyLhecaHid (pachyLhecaliina); (2) non-trabecular or fascicular (StylophyLlina): (3) minih'abecular (Caryophylliina); and (4) !hick-lrabecular microstruclural groups (Roniewicz & Morycowa 1993). Triassic corals showed diverse growLh forms. i.e.. solilaJ)'. phaceloid (see Glossary). and vari ous colonial forms representing diverse integration levels (cerioid. !hamnasterioid. meandroid. plocoid), bUI invariably possessed epithecal walls. Simple epitbecalholotbeca. - Pellicular epilheca was the moSI common wall. microstruclurally documented in aboul len families ofcorals ofminitrabecular. Lhick -trabecular and non-trabecular, fascicular septal microstructure (e.g.. Reimaniphyl liidae, Margarophylliidae. Procyclolilidae. Omphalophylliidae, Tropiastraeidae. Am· ioph)'JJlIm-group. Slylophyllidae. and Thamnasleriidae). Mature epitheca is known chiefly in !he families: Volzeidae. Protoheleraslraeidae. Procyclolitidae. Cycliphylli idae, Reimaniphylliidae (Cilifia), i.e.. in minilrabecularcorals. Pachytheca is known in Zardinophyllidae. ACTA PALAEONTOLQGICA POLONICA (44) (2) 147 12. A_71l«ocyalhus maclms(Goldfuss, 1826), Jurassic (Toarcian). France. MNHN M.OI263. Epithecal a:nIlPm UllaImJ view. B. C. DiscoC}'QllrllS tlldtsii (Michelin, 1840). Jurassic (Bajocian), Croisille. Cal- Fn.nce, MNHN M.OOO86. Distal (B) and proximal (C) views; epitheca in concentric folds. D--H Trochoryothus ra....son! Poonal~s. 1874. Recent, off Venezuela. 12"46·Nn0"4I'W. 201 m, ZPAL tLX' IV!O. Distal (D) and lateral (E) views, epithecal cover incomplete. F. Afragmen! ofthe calicular rim .. I.COOW1 zone belween the wall and septa (see the text); nOle a shatp rim ofthe epitheca G. A frag _ -.piried showing centripetally orienled fascicles of fibres of the epithe<:a; etche Number of genera 50 30 20 10 T"""'" Ju ComposHe epilhecal wall. - The only wall oflhis category known in the Triassic is an epithecal-stereomal wall in solitary and phaceloid st)'lophyllines. Early Jurassic-Early Cretaceous AI the Triassic-Jurassic boundary the majority of the then dominant epithecale scleractinians became extinct except for !.he stylophylLids. and were replaced by new coral groups that comprised faunas of different morphology and microstructure (Ro niewicz & Morycowa 1989, 1993). The replacement faunas contained numerous solitary corals (cylindrical, ceratoid, trochoid or discoid; see Duncan 1867-1868; Beauvais 1986); phaceloid corals became relatively rare, although well differentiated taxonomically (compare Beauvais 1986). The phaceloid epithecate corals re-appeared as an important faunal component not ear lier than lhe Late Jurassic. In microstructural plan, !be change at the Triassic-Jurassic boundary was even more dramatic, as practically all known earlier microstructural groups at !be family level disappeared (Roniewicz & Morycowa 1989, 1993). It led to a great taxonomic change in the coral faunas. 1be impact of !be mid·Cretaceous faunistic crisis upon corals, expressed as a taxonomic impoverishment ofa fauna still Late Jurassic in character, resulted in a conspicuous reduction of epithecatc solitary and phaceloid corals (Fig. 13). In the Early Jurassic-Early Cretaceous interval the following types of epithecal wall were common: Simple epithe<:a/holotheca. - This type of wall was common in hololhecal corals. These corals belonged to the families that range 10 the Early Cretaceous e.g., thamna steriids, microsolenids, styHnids, haplaraeids. Since the Aptian. discoid corals devel oped with concentrically wrinkled undersurfaces (morphological features ofepitheca). ACfA PALAEONTOLOGICA POLONICA (44) (2) 149 Fig. 14.Aplosmilia sp., Jurassic (Oltfordian). Franl;:e, ZPALH.xvun I. A. General view. B. Enlarged frag ment. SeplOthecal wall (sp) covered with thick leclura (I). Thin seclion. Here also belong the Aptian faviine corals Cyclophyllopsis (AUoiteau 1957) and Dimorphocoeniopsis (Zlatarski 1967), and the Aptian-Cenomanian Cyclas/raea (AI loiteau 1957; Ziatarski 1970; Gill & Lafuste 1971). Mature epitheca is observed in the Intersmiliidae, Donacosmiliidae, and Cladophylliidae. Typical pachytheca is observed only in the Amphiaslfaeidae. Composite epilhecal walls. - Epitheca combined wilh epicoslal dissepiments ap peared for the first time in Ihe Early Jurassic (Monllivahiidae) and became common in the Late Jurassic (Montlivahiidae, Fig. IOA-D; Misistellidae and Placophyllia; a wall determined as epicostal paratheca in Eli<1Sov<1 I976a: figs 1,2; pl. I: 1-3; pI. 5: I; pI. 7: I). Beginning in the Middle Jurassic, there are common cOffi(X>site walls with thin epitheca and trabeculOlheca or septotheca (Dermosmiliidae, Smiloslyliidae). Epitheca (identified morphologically) covered skeleions of Ihe earliesl caryophylliids: e.g.• the 150 Epjlhual~ sckroctiniQlU: RONlEWlCZ &: STOlARSKJ trochoid corallum ofToarcian 'T'McOC)'athus, or the lower surface ofdiscoid Bajocian DiscoC)'olhus (Fig. 12A, E). 1be walls ofsome JurassiC-CrelaCeOUS corals. considered up to DOW to be epithecal, differessenlially in structure. Here we place a wrinkled, probably trabecular wall (wil.h a peripheral Line made of dissolved centres of calcification joined to the midline of septa. as in the AabeLlidae) of the archacosmiLiids (Early Jurassic; Melnikova 1975: pI. I: Iv; Beauvais 1986: pI. 2: 3d), and septothecal wall with thick tectura in the rhipidogyrids (Fig. 14). Late Cretaceous-Recent Since the Lale Crelaceous. a difference in morphology ofcoralliles has been mark.ed between shallow-water and deep-water corals. Beginning with the Turonian, corals in deep-water environments (Type C. MjddJe Shelf, see Droscr et al. 1993) became a conspicuous element in the faunal spectrum. These were caryophyUHoe corals (LateCrelaCeous, see Alloiteau 1957;Turlliek 1978; Nielsen 1922), and later, dendrophylLiine corals (Paleogene, see Wanner 1902; Nielsen 1922; Aoris 1972). However, among these corals, epithecal walls are no longer com mon (less than 5% of cacyopbylliine genera). The most progressive groups of the Caryophylllina (Le.• the Aabellidae, Turbinoliidae. and Caryophylliidae) developing in the Cenozoic. nearly completely lack epitheca. 1beir walls are trabecular or septo thecal, and often covered with tectura (Stolarski 1995). 1be Late Cretaceous shaUow-water coraJ assemblages closely resembled those of Lbe Early Cretaceous in Lbeir taxonomic composition (see EJjoUov~ 1991. 1992; LOser 1989, 1994; Baron~Szabo 1997; Baron·Szabo & Fernandez-Mendiola 1997). Colonial corals dominated; some of Lbem had holotheca. Epithecate phaceloid and solitary cor als became rare with the exception of various discoid fonns with epithecallower sur faces (e.g., the large group ofcunnolitid corals ranging from the Coniacian 10 Maas lrichtian, see Alloiteau 1957; Tum~k 1978; Beauvais 1982). Also during the Tertiary, epithecale solitary and phaceloid corals were rare in shal low-water environments. Some of them had epilhccal walls Gudging from their mor phology). e.g.• Paleogene faviid Rhabdophy/liopsis (Alloileau & Tissier 1958) or Liptodendrofl (Eli&v~ 1991). 10 the Cenozoic, the following types ofepithccal walls have been recognized: Simple epilheca/holotheca. - Pellicular epilheca is known in prolocoraUiles of Gardinertidac, some Guyniidae and Rhizangiidae (Culicia), some Poritidae (Porites: JeU 1981: pI. 8: 4-6). some Caryophylliidae (Po/ycyalhus, Fig. 3A). Epitheca appar ently is also developed in early ontogenetic stages of Fungiidae (Fungia anthocauJus, see Vaughan & Wells 1943). Mature epitheca bas been noted only in aduh stagesofRe cent Cu/icia (see Chevalier 1971: fig. 65) and in some caryophylJjines: in Recent Garoineria (see Barnes 1972; Stolarski 1996; herein Fig. 7C-D). and three guyniids: Guynia. Schiz.ocyalhus and Temnotrochus (see Stolarski 1997). Composite epithecal walls. -1bese walls are common in shaDow water corals thai retain epithecal prolotheca. 1beir hololheca or epitheca are combined with syoapti culothcca. trabcculotheca and/or scptotheca; Miocene mussiid Syzygoplly/lia has an epithecal·parathecal waD. Recenl Manicina areo/ala shows that the holotheca may ACTA PALAEONTOLOGICA POLONICA (44) (2) 151 cover more or less completely the colony lower surface depending on the shape ofthe colony; in conical colonies the holothcca may cover nearly the whole lower colony surface (Barnes 1972: fig. la), or may fonn rings, or be developed only proximaUy (Fig. II), whereas in colonies with a convex caLicular surface and nat lower surface, the holotheca is developed as a horizontal sheath (Fabricius 1964). Composite epi thecal walls are known also in some caryophylliids (epithecal rings on the septothecal wall in some species of Trochocyathux, e.g., Eocene T. hyau; Vaughan, 1900 and T. uber Vaughan & Popenoc, 1935, and Recent T. rawson;, see Fig. 12D--H, and in Paracyathus, e.g., in Eocene P. beJlus Vaughan, 1900). Epltheca In ontogeny A primary epilhccal prototheca sometimes extends into posllarval stages as an epi theca. In some corals, the epitheca continues as a thin lamella from the basal plate to tbeuppercorallum part (e.g., some Rhizangiidae), but more frequently it is discontinu ous, or lacking in adult stages (Chevalier 1987). On the assumption that the ontogeny of the wall in Cordilleria and some other corals (zardinophyLLids, guyniids) is typical of most epithccate corals, and considering Chevaljer's remarks on extension of prolothecal epithccal structure into the adult stages, we regard a purely epithecal wall III post-protothecal stages in fossil corals (with inaccessible proximal portion) to be in dicative of their having epithecal prototheca. In me bulk ofcaryophylliids, a marginothccal prototheca develops. During trabe wall ontogeny two modes ofdevelopment have been observed: (I) in some taxa lite marg.inotheca extends into the adult stage. whereas in others (2) the marginotheca JqJI.aced successively by trabcculotheca and septotheca (Stolarski 1995). In some IDa the trabecular wall is combined in the adult stage with the epitheca interpreted Ilac • rudimentary element transferred from the juvenile to the adult stage. GcoenJJy speaking, the wall structure at the posHuvenHe stage manifests the main f~ ofits early ontogenetic stage, Le., the presence ofeither fibrous or trabecular prate:cbt.a. This allows discrimination ofa number of patterns ofwaU ontogeny typi- -..orne Recent and also ofsome important groups of fossil Scleractinia (Fig. 15). 1lrtollo\\109 review chieny concerns phaceloid and soljlary corals, as data on colo _lXJrab are scarce. P'a!ft'1I A -Theprototheca is epithecal. In the adult stage, the wall is purely ribrous; cpdx:cal caJjcular rim may fOnD a distal tube of various length. Ln the adult stage, IIf*\ £rom pellicular epitheca (especially common in the Triassic Rcimaniphylliidae, ~yJliidae,and some Procyclolitidae), there is a tendency to fonn thick walls. 1DClude various types of mature epitheca, pachytheca, and epithecal-stereomal 1be dislal septal margin often has a peripheral depression. The pattern is com ID the Mesozoic, chieny in the Triassic (ProtohcterasLreaidae, Volzeiidae, some :i1=.::'I.~"')'LLiidae.some Procyclolitidae, Stylophyllina. Zardinophyllidae) and in the Oadophyltiidae, Placophylliidae.lntersmiJiidae, DonacosmiJiidae, Arnphia : ad others). In the Recent, this feature is observed in a few genera (Ctllicia. GIn6wria. GU\'I1ia, Schi'locyatlms and TemllOiroclms). 15' Epithecate scleraelinialrs: RONlEWICZ & STOLARSKI Ul ::::l F\abellidae aw u f'5w 0:: U u Ul Ul ~ ::::l ...., -- Thecocyalhlidae u Ul Ul FIRSTGRAOE SECOND GRADE THIRD GRADE FOURTH GRADE Fig. 15. Evolution of the sdeml;tinian edge-woe (four grades) eJlpres5Cd in tcnm of wall development (five OIIlogenctic p;lllems A-E). The grades are shown as spindlc-diagmms which illustrate the relative spread ofcor als in shallow- (bnght ponion of the spindle) and deep-water environmenlS (dark portion): IlOIlO scale. First grade: edge.zone originally lacking. epithecal wall throughout Olllogeny. Second grade: variable range of the edge-zone: epitheca1 or tr.lbecuJar prolOlheca. and adult walls of different types (parotheca1. lnlbeculo-seplo thecal. synapticuJolhocal) combined with cpitheca.. Third grade: edge-zone fully developed. oflCn in\'cstmg the whole ~'Ofllllllm and producing tectum; trabecular prolOlheca and adult walls. Fourth grade: edge-zone redoced in range. producing tectum; margioothccal wall. The line linking Volzeiidae-ThecocyaLhidao-Caryophylli idae-F1abellidae represents an evolution of lhe SU1ICIUru! plan afme Caryophylliina and at the same time illllS lr.I.lCS a 5trnligr.l.plucal scqucoce of presumed 5ICps in phylogeny of the 5Ubordcr. ACTA PALAEONTOLOGICA POLONICA (44) (2) 153 Pattern 8. - The protomeca is epithecal. The posl-protothecal stage shows a pel licular epilheca, in places reduced 10 epithecal rings, bUI generally occurring in com posite epimecal structures. The septa are exsert. and me calicular rim is marked by me peripheral elevation of endotheca. It is common in the Jurassic-Cretaceous family Montlivaltiidae and occurs also in Recent colonial corals with epithecal prolOtheca. e.g.. Poritidae (Porites, seeJell1981: pI. 8). Pattern C. - The prololheca is trabecular (marginotheca). In post-protothecal stage. the wall is trabecular (either trabeculothecal or trabeculo·scptothecal) or synapti culothecal. Pellicular epilheca occurs in posl-juvenile stages and epithecal rings lend to be reduced. [n the Mesozoic, the panem is common in the Dennosmiliidae, Smilostyliidae, Archeosmiliidae and supposedly in Thecocyathidae (protothecal stages not examined duectly due 10 recrystallization): in the Mesozoic-Recent interval it is known in the F3viina and Dendrophylliina and some Caryophylliidae (Parac)'atlllls. TrocllOC)'atJIIIS). Pattern D. - The prototheca is trabecular (marginotheca). The post-initial trabe eulOlhecal wall may be replaced in the adult stage by a septotheca. The wall is often cov ered with tectura. Generally. epitheca is lacking, but sometimes relict rings may be present. The panern is dominant in the Cenozoic Caryophylliina. At leasl some Rhipi· dogyrina (Jurassic-Crelaceous) probably also had this omogenetical pattern; however, the microstructure oftheir prolothecal slages has not been examined directly. The indi rect evidence is the presence of the epithecal wall in the phaceloid genus Placophyllia I family Placophylliidae Eli<1.~ov~, 1990) exhibiting the neorhipidacanth type of the septal microstructure (Eli~~ov~ 1976: pI. 2: 2; 1990: pl. 2: I) typical of the suborder. Pattern E. - The prototheca is trabecular (marginOlheca). The adult wall is margi nothecal or. rarely. trabeculothecal. Tectura may develop. This pallern is known exclusively in Flabellidae sensu Stolarski (1995). A similar pattern (wall constructed ofa palisade of vertical spines in initial stage and trabeculae lD aduh skeletons) is known in the Pocilloporidae and Acroporidae. Wall patterns versus edge-zone development Vaugban & Wells (1943) and Wells (1956) noted that enlarging the edge-zone causes reduction of the epithecal wall. Wells (1956) defined the edge-zone as a column wall outfold extending over the calicular rim, and containing a continuation of the gastro vascular cavity. The edge·zone is developed in some solitary and phaceloid corals, bereas in colonial corals it is transfonned into coenosarc. The calicoblaslic layer of the edge-zone has potentially the same secreting capacity as the column wall of the polyp. and produces the extra-calicular prolongation of sepia (coslae), dissepimems MJd sclerenchyme. The edge zone's ability to develop external sclerenchyme is highly differentiated. lD some coral groups the edge zone covers the skelelon and does not produce the cJ:lrnCalicular sclerenchyme at all. in some groups il produces sclerenchymal thicken g ofextracalicular prolongation of skeletal elements. and in a few coral groups. the 154 Epithu61e scluoctimans: RONIEWICZ & STOLARSKJ edge zone of a high skeletogen.ic potential forms a panicular structure covering the wall. i.e.• tectura.In this section. we present the stratigraphic distribution ofcorals de veloping an edge-zone and their ability to form extra-caticular sclerencbyme. Paleontological dala and information on waH pallems in Recent corals allows the following gradation in the developmenl of edge-zone within the Scleractinia to be traced (Fig. 15). First grade. - Polyp entirely surrounded by an epitheca. edge-zone absent. Pattern A ofskeletal ontogeny. Mainly Triassic and Jurassic genera, some reaching the Albian; occurrence in shallow water deposits. In the Recent known as relict faunas in deep wa ter or cryptic environments. Second grade. - Temporary covering ofthe dislal portion ofcoraJJum with edge-zo.. ne. alternating with its withdrawal up to the caHcular rim. This resulls in the formation of an incomplete epithecal wall or epithecal rings alternating with paratheca, trabe culolheca. synapticulotheca or septolheca. Generally. the edge-zone lacks or has only a smaU ability to form extra Development and decline of scleractlnlan epithecate corals Transformations of scleractinian faunas The extinction event al the Permian-Triassic boundary eliminated the last remnants of the Pennian rugosan fauna. Some cryptogenic coral groups (pachythecal, minilrabe cular, thick-trabecular, and non-trabecular groups, see Roniewicz & Morycowa 1993) soon entered abandoned niches and in a span ofabout five million years became a sig nificant elemem of shallow-water benthic communities. These groups constituted the framework for the Mesozoic scleractinian fauna. Among the earljcst scleractinians there is a considerable percentage of solitary fonns but frequent are also colonial, highly integrated corals. in the Triassic, scleractinians with simpleepitheca (including bololheca) prevailed. This fauna resembled coral faunas of the Paleozoic due to common occurrence of epithecate taxa and thus similar polyplcorallum relationships. TIle presence of the epitheca as a main Slructural element in subsequent coral faunas supports the hypothe sis ofa continuation ofthe same architectural style across the P-T boundary (Stolarski 1996). ACTA PALAEONTQUXiJCA POLQNICA (44) (2) "5 The crisis at the Triassic-Jurassic boundary elintinated the majority of the early scleractinian genera with a Paleozoic typeofpolyplcorallum relationship. In the Juras sic, some survivors from lhe Triassic (stylophylLids) and descendants of zardino phyllids (amphiastraeids, intersmiliids, donacosmiliids) retained their primary mor phology and microstructure. In addition to these successful coral groups without edge-zone(First grade), there were some new groups (montlivalitiids, dermosntiliids), which eIDibited an enlargememofthe edge-zone (decline ofepitheca). This edge-zone had Iintited ability to produce extra-calicular sclerenchyme (Second grade). and co-existed with an epithecal wall. The families mentioned flourished in Jurassic-Early Cretaceous shallow-water environments. The Second grade in edge-zone development was attained by corals of many Me sozoic groups, which differ from each other in their ontogeny. In these corals, epitheca, ifdeveloped. was rudimentary; in some groups it was confined to proLOthecal stages, while in others it remained as a relict element in post-initial ontogenetic stages. This epitheca was retained by Cenozoic shallow-water corals and a larger group of deep -water corals (DendropbyUiina) that began in the Late Cretaceous. The Third grade in edge-zone development staned as early as the Jurassic (Rhipi dogyridae).ln rhipidogyrids, an edge-zonecovering large portions oftheeoraII urn was highly active in the production of extra-calicular sclerenchyme. Other groups having an extended edge-zone were represented by the Caryophylliina. with Iheir expansion to deeper waters beginning as early as the Late Jurassic. oleworthy is the evolutionary trend initialed in the Late Cretaceous by the Aabellidae, which involved some reduction of the edge-zone co-occurring with • complete loss of epitheca (Fourth grade). Mesozoic environments that were on the one hand favourable to survival ofconser \-aLive faunas, on lhe other hand induced imponant changes in the ontogeny and polyp anatomy of various phylogenetic lines. The appearance of composite epithecal walls aod non-epithecal walls (trabecular walls. tectura). testifies to ontogenetic evolution and the loss ofthe Triassic pattern (Pattern A). In the Jurassic genus Chomatoseris (ap pearing in the Lias. Beauvais 1986), a complete investment ofthe skeleton wilh a liv 109 tissue may be observed for the first time (see Gill & Coates 1977). These transfor mations in the wall strucrure and/or polyp-skeleton relationships through geological bIDe testify to the growing importance ofthe polypal edge-zone. The great number of phylogenetic lines experiencing structural transformation ofwalls suggests directional kctive stresses in Triassic and Jurassic cora) environments. Early in the Cenozoic time, phaceloid and solitary epithecatc forms almost com pletely disappeared. At the same lime, the role ofcolonial corals increased in shallow waitt assemblages, especiaUy fast~growing zooxanthellate forms. However. epitheca ranained imponant in some colonial corals, either as prototheca, or as a more or less complete holothecal coating of adult colonies. Shallow-water colonial corals. which appeared at the beginning ofCenozoic rime and aduc\'tld an unprecedented evolutionary success (e.g., the Acropora Emergence ofRosen 1993). displayed adaptations confined to agitated water conditions (acroporids, pocillo ponib. poritids. fungiids). The resulting colonies are characterized by the highest degree of '*iJiaion ofpolyps, thus producing strong, porous. quickJy built skeleton which is totally ren:d by lDOxal1lellate Living tissue having a high regeneration potential. 156 Epjl~cau sduat:tinians: RONlEWICZ &. STOLARSKl Mesozoic success of epithecate corals The successes ofcorals with simple epitheca observed in Late Triassic and Lale Juras· sic apparently were ecologically conlCOlled. The impressive and intriguing history of epilhecate corals was connected above aJl with the temporal flourishing ofsolitary and phaceloid growth foons (Fig. 13). The paleontological record suggests that a direct relationship existed between the radiation of phaceloid corals and the expansion of shallow-water environments of fine-grained, muddy and sandy limestone deposition on carbonate platforms (espe cially those of Late Triassic and Late Jurassic age). Conversely, their disappearance correlated with the decline of these environments. Fine-grained sedimentation led to the prevalence. on a global-scale, of relatively unstable sediment bottom. Sedi mentological data indicate that. as a rule. calcareous sediments rather quickly consoli dated. However, laking into consideration that micritic limestones were deposited as loose micritic panicles (Gruszczynski 1986), we assume that bottom surfaces re· mained rather unstable causing temporary turbidity of water during stonns. Thus, abundant limy sedimentation, unstable substrates and lUrbid waters resulted in the de velopment of a unique coral environment. The analysis of some Upper Jurassic West European reefs by Insalaco etal. (1997) indicates that phaceloid coral thickets (buill of non.-epithecate Aplosmilia) developed in a depositional environment of pure micritic limestone showing no traces ofearly cementation. Other examples ofphaceloid coral assemblages within environments of fine-grained micritic sedimentation origin are from the Upper Triassic of Lbe Alps (epithecate Reriophyllia assemblages, see Stanton & AUgel 1989, 1989), from the Upper Jurassic of Poland (epithecate Calamophyllia assemblages, Roniewicz & Roniewicz 1971), Ponugal, Spain, Switzerland and France (bibliographical data summarized by Leinfelder 1993). Given the deficiency ofhard substrates suitable for settlement of planulae, and the continuous race wiLb sedimentation, growth forms may have played an important role in the survival and propagation of species. Phaceloid growth forms assumed this role in Mesozoic carbonate platform environments (Ronjewicl. 1989b). In rhose environ ments, two extreme coral life-strategies may be differentiated that are analogous to the soft-bottom strategies of bivalves, i.e. 'mudstickers' and 'recliners' (SeHacher 1984; Machalski 1998). Phaceloid epithecal and solitary non-discoid corals adopted the soft-bottom strategy of 'mudstickers' where sedimentation rates increased, whereas colonial lamellate and/or massive corals and discoid solitary and colonial corals, the 'recliners', where sedimentation rates lowered. [n coral 'recliners', one may consider the possible adaptive significance oftheir epithecalholotheca. In juvenile colonies and at the perimeter ofadult lamellate colonies in different suborders, the holotheca is the most external element of the colony and serves as a 'bedplate' for the development of newly formed septa. Thus, its development might be important for corals laying on the sedimentary bottom (snow-shoe effect). The decline ofepithecate corals - possible causes Major ecological changes at the Triassic-Jurassic boundary resulted in Lbe extinction of a majority of corals having a primary wall structure. TIle number of taxa having a polyp initially enclosed in epithecal wall (First grade) declined. especially the repre senlatives of the Zardinophyllidae, Voluiidae, Reimaniphylliidae, Cycliphylliidae, ACTA PALAEONTOLOGICA POLONICA (44) (2) 157 and others. Free niches soon became occupied by corals with new types of ontogeny and a new mutual relation between [he polyp and skeleton, i.e. corals that have devel oped an edge-zone (Second and Third grades). In turn, these successors as well as some relict but abundant coral groups with an epithecal wall similarly, adversely re acted in response to the environmental crises at the end ofthe Jurassic, and later during the middle of the Cretaceous period. These were, among others. the epismiliids, amphiastraeids, and dennosmiliids (Roniewicz & Morycowa 1993). As a consequence ofthese environmental changes. phaceloid and solitary shallow-water epithecate cor als never flourished after the mid-Cretaceous crisis. Adverse responses to environmental changes were not observed in colonial holo thecal corals originating in the Mesozoic (e.g., Faviidae), which exist today in shallow .... aters. though Recent coral environments, confined to the near-shore zones and, at most, to the hard substrate. differ from those ofthe Mesozoic, which developed mostly on 5ediment bottom, and presumably at greater depths (Geister & Lathuiliere (991). This suggests the high adaptability oftheir colonial mode oflife to survival in shallow ..aters. A general decline of epithecal forms in modem seas can be seen in both shallow water and deep water environments. It has been caused by two parallel processes dur 109 the Cenozoic, influencing the growth-forms exhibited in modem fauna: (I) in shallow waters, the process of elimination of solitary and phaceloid corals utber than the expansive Fungia which has a skeleton fully covered with living tissue, Md a few phaceloid genera living in sheltered conditions, all of which lack epitheca; domination by colonial highly integrated colonies. (2) in deep waters, the process oftaxonomic increase ofsolitary forms which, with rarecxccptions (gardineriids, some guyniids), have skeletons covered by living tissue, ather completely devoid ofepitheca or retaining it in a relict form in late ontogenetic ges (ontogeny of Pattern E and D, respectively); colonies are represented by zig -branch forms (uniserial erect forms ofCoates & Jackson 1985). Jt may be inferred that Triassic and Jurassic epithecale solitary and phaceloid ~ developed in environments with low rates of mechanical deslruction. This cooclusion is based on the fact that regeneration potential ofepithecatecorals is rela u\el) low due to a lack ofan edge-zone, i.e., the tissue which could cover the exler aal surface ofthe corallum and repair injuries, or to build the strengthening layer, i.e., IIC:CttU'a It is worthy ofnotice, that the ability to repair injuries in phaceloid corals is IkOIDparable to that of colonial branching corals having the total surface covered nh (malJ polyps. In epithecate phaceloid corals, only the tips of branches (coral Iiu: I bear the living tissue, I.e., the polyps; the death of the polyp means inevitable dea.uuction ofthe naked skeleton. For the reason of the low regeneration potential of zoic phaceloid epilhecate corals, their life conditions can hardly be compared ch those ofeasily regenerating Recent branching corals (e.g.. Triassic Retiophyllia Recent Porites. see Bernecker et al. 1999). Perhaps the ability to form a thick IrdUra by the Rhipidogyrina (phaceloid Aplosmifia, solitary Rhipidogyra and colo~ 8UI forms homeomorphic with Recent shallow-water Eusmiliinae) could explain the npd upansion ofthose corals in the latest Jurassic and in early Late Cretaceous en Y1tOCllDCDts (Elia~ova 1973 and 1991. respectively), and their colonization ofwaters 01 Igber energy. 158 Epltherou scluactinitms: RQNIEWICZ &: STOLARSKI 10 modem shallow-waler environments, solitary and phaceloid epithecate corals could not survive due to high rates ofbioerosion accomplished by various organisms, i.e., microborers harmful 10 their bare skeletons and. especially, grazing molluscs or fish predators which could easily kill their isolated polyps. In Mesozoic material we observed microborings (endolithic algae) in surficial skeletal parts, boring bivalves and polychaclcs in massive colonies. but have never discerned the traces ofgrazing or ganisms on any coral skeletons. This observation agrees with the statement ofStanton & FlUgel (1987) that various organisms from the deslrOyer guild (Fagerstrom 1984) expanded no earlier than latc in the Mesozoic and in the Cenozoic. TWo factors may cause lhe level of biocrosion on the sea bottom to be low: lack or unimportance of bioeroders (cause of evolutionary or ecological nature) or high rate of sedimentation and quick burial of exposed skeletons (cause of sedimentological nature). Benling (1997) has shown an inverse proportion of intensity of bioerosion to sedimentation rates in Jurassic coral environments. We assume that a bulk ofTriassic and Jurassic phaceloid and elongated solitary epithecate corals lived in environments of high-rate sedimentaion. Apart from their growth fonn. it is supported also by low bioerosion of their skeletons. In shallow water. the main factor causing edge-zone extension may be a bioerosion, wbereas in deep waler environments below the calcium compensation depth (CeO) a factor ofchemical corrosion ofcalcareous skeleton must be considered. Thus, an es cape. from the epithecal state OOsen'ed in many coral groups might be caused by the envi ronmental stress leading to the elimination ofepithecate corals and the developmem of corals provided with an evolutionary novelty, a protective edge-zone. Naturally, an ex tended edge-zone may be an effective protection only against endolithic microborers, but ineffective as a protection against mollusk., echinoderm and fish predators, which are important destroyers in modem shaUow-watercoral environments (compare Hutchings 1986). The role ofanimal bioeroders in the post-Mesozoic red algae evolution has been a matter ofdiscussion by Steneck (1983). The decline ofMesozoic solenoporacean red al gae is analogous to the decline ofthe epithecate corals. Thus, bioerosion, increasing sig nificantly since Late Jurassic (Bromley 1994), appears to be a powerful factor in the turnover and evolution ofsome Mesozoic/Cenozoic organisms. The success of Cenozoic corals The most successful corals in the Cenozoic belong to the acroporids. pocilloporids. poritids. fuogiid and deodrophylliid corals. as well as multidirectionally radiating caryophylliine corals. 1be first four groups are shallow-water and colonial except for the solitary FlU/gin. the latter two are predominantly deep-water. moslly solitary cor als. in the acroporids and pocilloporids. any epithecal wall seems to be lacking. In the other groups, the epitheca is rudimentary and edge-zone evolution resulted in a maxi mum covering of the skeleton by living tissue. Judging from its morphology, in fungiids a relict epitheca has been retained in the protothecal stage (see Vaughan & Wells 1943). In the dendrophylliids. the prototheca is trabecular. and theepitheca initi ated during the early post-larval stage may also extend into adult slages in some soli tary fonns (e.g., TlJecopsammia). but the majority ofcorals have skeleton completely devoid ofepitheca, and covered with living tissue, up to a complete envelopment ofthe corallum (Heteropsammia). ACfA PALAEONTOLOGICA POLONICA (44) (2) 15' In the caryophylliine phylogenetic stem, development of lhis tendency is observed throughout its history (Fig. 15) and is illustrated by the following stratigraphical distri bution ofsuccessive fonus: Triassic - epitheca well developed (Volzeiidae); Toaracian - epitheca well developed (Thecoc)'orhus); Bajocian-?Paleocene - reduced epilheca CDiscocyathus); ?Oxfordian-Recent - rudimentary (Troc1l0CYOlhus) or lacking epi lheca, The turbinoliids represent the final stage of the edge-zone expression (?Albian, \taastrichtian - Recent). Their coral1a are fully covered with Living tissue and lack q)ltheca, although traces of it can be seen in some Paleocene forms that probably rep resent a separate evolutionary line (see AJloiteau & Tissier 1958). Covering of the corallum by living tissue resulted in developing of automobility (see Fabricius 1964: Gill & Coates 1977). The expansion of living tissue beyond the thecal rim increased the skeletogenic polyp surface, and this. supposedly. was responsible for an unparalleled evolutionary plasticity within the Recent Caryophyllioidea. This is a group ofcorals that now occu pte:. most Cenozoic environments available to corals, Thus, it includes shallow- and deep-water azooxanthellate species, as well as zooxanthellate, hermatypic forms. It is also the most taxonomically diverse group ofScleractinia, represented today by about 7Q genera and more than 400 species (Cairns 1997). Differentiation of ontogenetical [;pes wilhin the traditional CaryophylHina (Pattern A, C-E) is also greater than that \IIllhin other suborders (Faviina: Pattern A, B, and C; Dendrophylliina: Pattern C). IOlilarly. there is a highly differentiated development of the edge-zone, as the border contains forms without an edge-zone, and some with an edge-zone ofvarying letogenetic potential (First to Fourth grades), showing various edge-zone-derived . e:letal adaptations to soft as well as hard substrates, Conclusions • In the history of the Scleractinia there are changes in wall structure, that show a trmdofmodification ofthe polyp anatomy, i.e., expansion oflhe edge-zone (First to Fourth grades), Triassic corals with complete epitheca and lacking the edge-zone Fmot grade) represent the starting point for further development'ofthe coral polyp. xtension ofa simple edge-zone lacking skeletogenic potential led 10 the formation . e:pithecal compound walls (Second grade). The secreting ability achieved by the edge-zone created a new condition: the capability offonning ofextra-calicular skel- deposits, e.g., tectura (Third and Fourth grades). The trend of edge-zone en .rgement is expressed in the phylogeny ofsomecoral groups (e.g.. Caryophylliina) iOd IS reinforced by general faunistic lurnovers caused by biOlic crises which elimi ..ded taxa (sometimes of higher ranks) with underdeveloped edge-zone. • llu:. trend was probably accomplished by a lransfonnation ofontogeny with the re- lion or elimination of epithecate stages. This process may be reconstructed ~ on the ontogenetic sequence exhibited by the Caryophylliina. This group has retamed the most primitive ontogenetic pauern (Pattern A) with epithecal prOto )CC3 which survived unlil the Recent together with a series of progressively trans fnmung patterns (Panern C, 0, E). Most post-Triassic CaryophyUioidea lost epi ~ gradually during the Jurassic. and entered the Cretaceous practically devoid of 160 EpitheclJle scleractiniafls: RONLEWICZ & STOLARSKJ epilheca. Radiation of the Cretaceous caryophylliines generated new phyletic lines, each of which was characterized by its unique skeletal organization. AJong with lhis development there persisted re(jet epithecate lineages ranging from the Triassic to the Recem represented by dwarf fonns. • The fact that most deep~wa!er caryophylliid lines are devoid of epitheca suggests that their migration from shallow water to deeper water look place after they lost the ability to form epitheca. • Modificalion of polyp anatomy and development of the edge-zone with transfonna tion of the wall structure occurred dramatically in corals confined to shallow water. In these environmems, older lineages of epithecate phaceloid and solitary form$ were eliminated during successive environmental crises (Triassic-Jurassic, Juras sic-Cretaceous, Early Cretaceous-Lale Cretaceous), which accelerated faunal turn overand resulled in selection ofpolyp organization. In contrast, colonial corals hav ing a poorly-developed edge-zone persist up to the present and retain epitheca in their ontogeny. Modem shallow-waler faunas also comprise corals with a well de veloped edge-zone (from the Second to Fourth grades). • I.n the Mesozoic, the environments of corals with simple polyp organization were carbonate platforms; their development in the Late Triassic, Late Jurassic and in the Early Cretaceous prolonged the survival of forms which lacked an edge-zone. and thus continued existence ofan ancient Paleozoic anatomical pattern. Even new post -Triassic corals that diversified during Late Jurassic and Early Cretaceous time, hav ing relatively well developed edge-zone (Second grade), retained epilheca as an ad dition to trabeculotheca and/or septotheca. The ecological driving force for evolu tion of non-epithecate corals in the Mesozoic was probably the increasing role of bioerosion in the coral environments. The edge-zone developed as a protective fea ture, which in the Cenozoic became a subject of intensive evolution. Today, the cor als with purely epithecal walls are known exclusively in deep-water or cryptic envi ronments where the slress caused by bioeroders is negligible. Acknowledgements Recent coral collections of the Institute of Paleobiology in Warsaw have becn augmcllled thanks to donations of Stcphen Cairns and Helmut Zibrowius. Antonio Russo made available his colh..'ction of Triassic corals from the Dolomitcs. To James Sorauf and Jeay Fedorowski we arc obliged for criti cism of the ideas presentcd here. and to Ann Budd and Brian Rosen for thcir remarks that helped us very much in ameliorating the last version of the text. We appreciate very much an encouragement and the help offered us by Stephen Cairns. Zbigniew Su;pe. made thin sections. Graiyna and Marian Dziewinslci prepared the macrophotographs (all from the Insitute of Paleobiology, Warsaw). Finan cial support was given by the Committcc for Scientific Research (KBN). grant 6 P20 I 034 05 to E. Roniewicz and 1. Stolarski. References Alloncau. J. 1952. MadJiporaires Post-Pal~ozoiques. I,,; J. Pivetau (ed.). Traltl de Pallontologle /. 539-684. Masson et C". Paris. Alloiteau. J. 1957. Contribution dla SYSllmariqlfl! dt'~ Madrlporairt'~fossilt'~. /.426 pp. Centre Nallonale de In Recherche Sdentifique. Paris. AcrA PALAEONTOLOGICA POLONICA (44) (2) 161 Alloiteau. J. & Dercoun. J. 1966. 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Dimorphocoeniopsis bttluvaisorum, une nouvelle es¢ce de Madreporaria du Clitace inferieur de la Bulgarie du Nord. - Comptes Rtndus de tAcadlmie bulgflre de Scie/lcts 20, 1317-1320. Ziatarski. V. 1970. eyclaslraea mtllellSis. nouvelle es¢ce de Ma Glossary Colonial corals. - Corals in which polyps are integrated to various degree (Coales & Oliver 1974). Corallites of colonial Scleractinia lIIay form cerioid. plocoid. dendroid. thamnaslerioid. and mcan droid colonies. Epitheca (Milne Edwards & Haillle 1848). - Wall built of calcareous fibres not organized into trabeculae. lIs outer pari is fonned in the apical part oflhe soft tissue fold (lappet cavity). The calcare ous fibres of the outer part are oriented distally. The inner pari of the epitheca, i.e.• epithecal Slereome. shows centripetal organization of fibres. Epitheca oftcn accompanies other skeletal struc tures in forming composite walls (i.e.• epithecal-dissepimelllal; epithecal-trabeculothecal. epithecal -septothecal; epithecal-stereomal in ---7 non-trabecular corals) but may also fonn the only coraJium wall. Holotheca (Hudson 1929). - Epithecal wall common 10 peripheral cora1tilcs ofa colonial eorallum. Marginotheca (Mori & Minoura 1980; Stolarski 1995). -A wall consisting of distally growing rninitrabeculae (---7 trabeculae). continuing inlo a median line of radial elements. Non-trabecular or fascicular corals (Roniewicz 1989a). - The term describing microstructural features ofcorals in which septa as well as the whole skeleton are organized into bundles of fibres that emerge on the surface as minute granulations about 30 j.lm in diameter. EXcluding the epitheca, the skeletal parts (septa. disscpimcnts. adaxial waU portions) are in structural continuity with each other. In septal spines. the bundles are elongate and diverge laterally from the axial pari ofthe septal spine. The elongated bundles resemble mini trabeculae in dimension but differ in lacking the trabecular ar rangement of fibres; their fibres are parallel to each other. The adaxial wall portion is built of multidirectionally oriented bundles and sealy fibre aggregates. This microstructure is known only in the suborder Stylophyllina (Cuif 1973; Roniewicz 1989a). Pachylbeca (new lerm). -A type of epithcca with a very thick inner layer showing characteristic modular structure. The modules are large and equal-sized bundles offibres that tend to fonn centred struCtures (peniciUate organization of fibres of Cuif & Gaulret 1993). Paratheca (Vaughan & Wells 1943). - Wall consisting of intercostal or epicostal dissepiments. Phaceloid corals. - Corals in which polyps are not integrated. although developed from single planula. Because of their lack of integration. phaeeloid corals are considered as pseudocolonies (Coates & Jackson 1985). Septotheca (Vaughan & Wells 1943 = pscudOlheca ofvon Heider 1886).-Wall developed by thick ening of the outer part of sepia. Solitary corals. - Corals with single polyps. whose most common condition is monostomodeal. Tectura (Stolarski 1995). - Extra-calicular sclerenchyme adhering to the outer corallum surface: deposited by edge-zone: growing centrifugally: fibrous or organized in trabeculae: surface smooth (porcel1aoeous). or corrugated. or covered by granulations. Trabeculae (Trabekeln of Pratz 1882 = poulrelles of Milne Edwards & Haime 1848: modified after Bryan & Hill 1942). - Continuously growing rods fonned by fibres (aggregated in tufts. Jell 1974). provided with an axis. and 001 divided into sclerodermites. For descriptive purposes. it is useful 10 distinguish two main size classes of trabeculae: minitrabeculae from 10 to 5O}.Im in diameter. and large (thick) trabeculae which are more than 50 flm in diameter. Scptaltraheculae may be arranged in a fan-like pattern or uniserially. Most Scleractinia have trabeculate scpta. except Stylophytliina (---7 non-trabecular or fascicular corals). Trabeculoth«a (Chevalier 1987: Stolarski 1995). - Wall consisting ofa trabecular palisade. inter rupted by radial clements.